[RandomTask]

You have to define 'highly modified'. What internal work is done? Some of the biggest mistakes with people running turbocharged motors involves fuel. Too many times will they try to up their boost without compensating with more fuel. The more air (higher boost) you're pumping into your motor the more fuel it requires. If you don't compensate you end up leaning up the motor. Lack of fuel can usually be compensated by adjusting three things-
1. Different (larger) Injectors
2. Higher flowing fuel pump
3. Duty cycle of the injectors (Time that they're open/spraying) -- Hard to fine tune with stock ECU's.

Also, has your ECU been reprogrammed? If not, may be it can only detect up to a certain boost pressure and after such cannot adjust the timing accordingly.

Another situation- If you have one, your MAT (Manifold Air Temperature) sensor could be bad, as such not detecting ambient air temp. If its on cooler days it may not be able to adjust the fuel accordingly.

In relation to the spark plugs I would keep with the recommended gap as specified by your car. Also, be careful to the fact that some kinds of spark plugs can't be gapped. I personally don't believe in all of those platinum +2 +4 and most other 'leading technology' spark plug. I've heard a lot about those denso iridium ones as well but am skeptical about them as well. For domestic engines, I know the inexpensive ($1.47 a plug) AC's work the best. (I've dyno compared them to Bosch platinums on my Monte Carlo and picked up 8HP)

"More Money In My Engine Then Your Car Costs..."
I can't understand if this makes you 'cooler' or dumb. If you did spend more money, you still can't get it to run right. So now you put all that money into a motor that doesn't run right... Just some friendly bashing-- I would like to point out, The HP to money line on a graph is not the same for all motors. So when you could spend $1k on one motor and only pull out 125HP, give me a grand to spend on a stock small block, I guaruntee I can pull up 200HP.